By John — Desalination News
A team at the University of Rochester has built a solar-powered desalination device that turns seawater into drinking water without discharging any liquid brine, instead leaving behind dry, recoverable salts — including, in follow-up work, lithium. The research, led by optics and physics professor Chunlei Guo, was published in the journal Light: Science & Applications.
The system centers on panels of “black metal” that have been textured with femtosecond lasers, giving the surface two properties at once: it absorbs almost all incoming sunlight, and it is intensely water-attracting, a trait the researchers call superwicking. A laser-patterned active region draws a thin film of seawater across the panel; as sunlight heats and evaporates the water, distilled fresh water is collected while dissolved salts and minerals are steered away from the active zone toward untreated “passive” sections of the same panel.
That routing step is the technical breakthrough. Most solar desalination research to date has been tested on simplified saltwater — sodium chloride and water — which forms loose, porous crystals that are relatively easy to keep clean. Real seawater is far messier: magnesium and calcium compounds tend to crystallize into hard, dense scale that can clog a device much the way mineral buildup clogs a kettle or showerhead, eventually shutting the system down. Guo’s team addressed this by engraving microscopic grooves into the panel surface and exploiting the “coffee ring effect” — the same physics that leaves a ring of concentrated particles at the edge of a dried coffee spill — to continuously carry salts toward the passive regions rather than letting them accumulate where evaporation is happening.
In testing with seawater samples from the Pacific, Atlantic and Indian Oceans, the surface reportedly kept cleaning itself, with fresh water extracted continuously while salts collected separately as solids rather than as the concentrated liquid brine that conventional reverse osmosis and thermal desalination plants must treat or discharge. Brine disposal remains one of the industry’s persistent environmental sore points, since discharging concentrated saltwater back into the ocean can raise local salinity and reduce oxygen levels for marine life.
A related advantage is what happens to the recovered salts afterward. In a second study, published in the Journal of Materials Chemistry A, the Rochester group embedded hydrogen titanate nanoparticles into the panel’s grooves to selectively pull lithium out from the other dissolved minerals. Testing this approach on water from Utah’s Great Salt Lake, the researchers recovered roughly half of the lithium present in the leftover salts — a notable result given that conventional lithium mining is energy- and water-intensive, and demand for the metal continues to climb with electric-vehicle and battery production.
Guo’s team says the approach is still at the proof-of-concept stage and has not yet been demonstrated at plant scale, so questions about throughput, capital cost and durability under continuous industrial operation remain open — the same hurdle facing several other solar desalination concepts that have shown promise in the lab but not yet reached commercial deployment. If it does scale, though, the combination of chemical-free operation, no brine discharge and a secondary mineral revenue stream would address several of the cost and environmental objections that have limited solar desalination’s role alongside mainstream reverse osmosis. The work was funded by the National Science Foundation, the Bill & Melinda Gates Foundation and the Worldwide Universities Network.
(Source: University of Rochester / ScienceDaily)